1. Field of the Invention
The present invention relates to a control device for a legged mobile robot.
2. Description of the Related Art
Conventionally, techniques for controlling an operation of a legged mobile robot such as a bipedal mobile robot have been proposed by the present applicant and others. According to the techniques, during a walking operation or other motions of a robot, a desired gait including a desired motion of the robot is generated in real time, and the operation of the robot is controlled to follow the desired gait.
For example, the present applicant has proposed, in Japanese Patent No. 3726081 (hereinafter, referred to as “Patent Document 1”), a technique of generating a desired gait of a robot wherein, in order to allow the robot to perform a continuous motion (motion not causing divergence that would throw the robot off balance), a cyclic gait in which a motion of the same pattern is repeated is set as a convergence target in the future of a desired motion of the robot, and the desired motion for each step of the robot is made to converge to the motion of the cyclic gait, to thereby generate the desired gait of the robot.
Such a desired gait of a legged mobile robot needs to be generated so as to be able to satisfy various kinds of kinetic or dynamic requisite conditions. For example, as to the leg motions, the ranges of movement of the joints of the legs are subject to mechanical restrictions, making it necessary to determine the desired motions of the legs within the ranges of movement of the joints.
Further, a zero moment point (ZMP) as a point of application of a floor reaction force acting on a robot should be located within a so-called supporting polygon which is determined in accordance with a contact surface of the robot leg with the floor surface. This raises the need to set a desired position of the ZMP or a desired value of the floor reaction force moment about a prescribed point of application to satisfy that condition.
Furthermore, in order to ensure a stable and continuous motion of a robot, it is necessary to generate a desired motion of the robot so that a trajectory of the desired motion converges to the motion of a cyclic gait in the future, as in the above-described Patent Document 1.
On the other hand, a legged mobile robot is configured such that, while it receives a floor reaction force as an external force via its leg coming in contact with the ground, it performs a dynamically feasible motion by the external force. Thus, in the case where a desired gait of the robot is to be generated in real time while the robot is in motion, it is desired that particularly a desired motion trajectory of the distal end portion of each leg of the robot (particularly the landing position and/or the landing time of the distal end portion of each leg of the robot) is efficiently and properly set under various kinds of requisite conditions as described above.
In general, however, objects that will be directly restricted by those requisite conditions which have to be taken into consideration when generating a desired gait of the robot differ from each other. Therefore, conventionally, a desired motion trajectory of the distal end portion of each leg would be determined in an exploratory manner, for example by repeating the processing of: firstly provisionally determining a motion trajectory of the distal end portion of each leg to satisfy a particular requisite condition that directly restricts the leg motion, then generating a desired gait of the entire robot in an experimental manner while determining a trajectory of the desired position of the ZMP and the like, and observing whether the generated desired gait satisfies other requisite conditions.
With this technique, however, it may take time to determine the desired motion trajectory of the distal end portion of each leg that makes it possible to satisfy various kinds of requisite conditions, in which case it may be difficult to determine a suitable desired motion trajectory of the distal end portion of each leg efficiently and in a short time.